1. Field of the Invention
The present invention relates to a method for preventing electrode deterioration in an etching apparatus used in the manufacture of semiconductors.
2. Description of Related Art
FIGS. 7A, 7B, 8A, and 8B illustrate a series of conventional treatment steps performed in a reaction chamber 10 of an etching apparatus used in the manufacture of semiconductors. The structure of the reaction chamber 10 will be described through reference to FIGS. 7A to 8B.
As shown in FIG. 7A, the reaction chamber 10 of the etching apparatus comprises in its interior an electrode 12 and a discharge component 14. The discharge component 14 is provided facing the electrode 12, and a high-frequency power supply (RF power supply) 16 is connected.
As is commonly known, the etching gas is usually introduced into the reaction chamber 10 through a plurality of vents made in the discharge component 14. When a high-frequency voltage is applied from the RF power supply 16 to the discharge component 14, whose vents are not shown in FIG. 7A, a plasma is generated between the discharge component 14 and the electrode 12. The high-frequency voltage is sometimes applied to the electrode 12.
The plasma thus generated is used to perform etching in the reaction chamber 10. This etching treatment will now be described.
First, the steps shown in FIGS. 7A and 7B will be described. As shown in FIG. 7A, a substrate 26 is put in place on the electrode 12 after being transferred from a load lock chamber (not shown) into the reaction chamber 10. Specifically, the substrate 26 is fixed on the electrode 12 by a clamping apparatus 28 or other such means. FIG. 7A shows how the substrate 26 is fixed on the electrode 12 by clamping the ends of the substrate with this clamping apparatus 28. In the steps discussed below, the fixing of the substrate 26 is accomplished in the same manner as shown in FIG. 7A.
The electrode 12 has a plurality of openings 24. These openings 24 are each connected to a gas line 22. As shown in FIG. 7A, the gas line 22 comprises a cooling gas line 20, and an exhaust line 18 connected to the cooling gas line 20 via a fourth valve 32. A turbo pump (TP) 40 and an exhaust valve 42 provided between this turbo pump 40 and the reaction chamber 10 are installed along the exhaust line 18. When this exhaust valve 42 is open, the exhaust gas inside the reaction chamber 10 is purged by the turbo pump 40.
Meanwhile, the cooling gas line 20 is connected between a cooling gas source (not shown) and the plurality of openings 24. This cooling gas line 20 is provided with a master valve 21, a pressure gauge 38, a mass flow controller (hereinafter referred to simply as MFC) 36, and a third valve 30, sequentially from the cooling gas source side to the openings 24 side. The above-mentioned fourth valve 32 is provided to a gas passage line (branched line) 23 that connects, or links, the third valve 30 of the cooling gas line 20 and the openings 24, and the exhaust valve of the exhaust line 18 and the turbo pump 40.
The substrate 26 is installed on the electrode 12. With the fourth valve 32 closed, cooling gas is supplied from the cooling gas line 20 to each of the plurality of openings 24. Usually, when the substrate 26 is being etched, the surface temperature of the substrate 26 is raised by heat from the plasma and the reaction heat of the etching, which causes the etching rate to vary and results in an uneven etching rate over the surface of the substrate 26. The third valve 30 is installed along the cooling gas line 20. Opening this third valve 30 and supplying cooling gas prevents the etching rate from becoming uneven as discussed above. The mass flow controller (hereinafter referred to as MFC) 36 and a pressure gauge 38 are installed along the cooling gas line 20, and the cooling gas flux and pressure in this cooling gas line 20 are controlled by the MFC 36 and the pressure gauge 38. Helium (He) or another rare gas is generally used as the cooling gas.
The master valve 21, the third valve 30, the fourth valve 32, and the exhaust valve 42 shown in FIGS. 7A and 7B are shown white when in an open state and black when closed. Similarly, the open and closed states of the valves 21, 30, 32, and 42 are shown white or black in FIGS. 8A and 8B. The structure of the gas line 22 is the same in FIGS. 7A, 7B, 8A, and 8B.
As discussed above, the film provided on the surface of the substrate 26 is etched in a state in which cooling gas is supplied from the plurality of openings 24 to the rear face of the substrate 26 fixed on the electrode 12. FIG. 7B shows how this film is etched on the surface of the substrate 26 using a plasma 34 generated by the procedure detailed above. The third valve 30 is open and the fourth valve 32 is closed along the gas line 22 shown in FIG. 7B.
Next, the treatment performed after the step in FIG. 7B will be described through reference to FIGS. 8A and 8B. The application of the high-frequency voltage and the supply of the etching gas into the reaction chamber 10 are halted to conclude the etching of the substrate 26. After this, as shown in FIG. 8A, the third valve 30 is closed and the supply of cooling gas to the openings 24 is shut off. The fourth valve 32 is opened, meanwhile, and the cooling gas between the third valve 30 and the openings 24 is purged to the exhaust line 18.
Then, as shown in FIG. 8B, with both the fourth valve 32 and the third valve 30 closed, the clamping apparatus 28 is released, and the etched substrate 26 is conveyed from the reaction chamber 10 to an unloading chamber (not shown). The series of etching operations to which the substrate 26 is subjected is complete at this point.
The etching of substrates is carried out repeatedly in the reaction chamber of the etching apparatus by the procedure described above. While an etched substrate is being conveyed to the unloading chamber, that is, during the so-called non-etching period between one etching treatment and the next, the surface of the electrode is exposed inside the reaction chamber. The openings in the electrode are also exposed inside the reaction chamber during this time.
In this state, there is a fear that components separated from the reaction product generated during etching will be adsorbed to these openings. There is also another fear that the openings will be plugged when the above-mentioned separated components build up on the electrode and these deposits fall or find their way into the openings.
The size, number, layout, and so forth of the openings in the electrode are designed ahead of time according to the uniformity of substrate etching and other such characteristics. Therefore, if deposits adhere to the openings as mentioned above, the size of the openings will change, and as a result there will be a substantial change in the number, layout, and other aspects of these openings. As a result, the efficiency at which the substrate is cooled during etching in the reaction chamber decreases, resulting in a change in the etching characteristics.